kjr6306

I'm in the beginning process of rebuilding my 70 350 short block. This will be on a tight budget with a goal of 400HP/400TQ.

What I have to work with:

Original numbers matching block bored .060 over already.
Original Forged crank.
Original forged "pink rods".

The block and crank have less than 1000 miles on them since the a previous rebuild that included the bore to 4.060. This was done around 1991 but all is still in good condition. The cylinder deck has not been surfaced as the engine and VIN code are still on the block.

My first question is what replacement pistons are available that get me back to the original 11.0:1 CR. I have looked at the TRW L2304F forged pistons. Will be using 64 cc heads. Are these suitable for my rebuild?

I am shooting for .040 Quench and will use a .015 Fel-pro head gasket. I am assuming a standard deck height of 9.025". Do the top of these pistons come to 9.00" @ TDC assuming factory crank and rods?

Once I get the shortblock done, I will concentrate on the heads, cam and valve train assembly. Thinking about Vortec heads or maybe some inexpensive Aluminum ones. Headers, and possibly a solider lifter cam. This car will only be driven 1000 miles per year to car shows, weekends cruising and an occasional trip to he drag strip.

Forgot to mention it is a 4 speed, 4:11 rear and M21. This is my first engine build so I am trying to learn as much as possible. Dealing with a lot of information overload right now...any help is appreciated!!!

Revi

I have a 70 350/350 that was rebuilt a couple of years ago. The block was not decked, the bores are .030 over. I used the L2304F pistons.

I have 10.4:1 c/r so I could run 93 oct. I'm using the original heads (ported), intake manifold, carb, etc.. I did change the cam to an XE-262H-10. It looks like a factory stock L-46 on the outside.

It dynoed at 341hp/387tq. The original cast iron intake and heads limit the top end.

A better set of heads and intake (as you are going to use) should give you the 400hp that you want.

If you obtain an actual 11:1 c/r you will need a fuel additive or race gas.

kjr6306

I will disregard the response from 2 broke as I am sure there are plenty of guys with stock LT-1's with 11:1 static CR using pump 93 octane fuel. From what I understand the more important number with regards to CR is the CR which is determined by the cam and the actual time in the compression stroke that the intake valve actually closes. I plan on using a cam that puts my dynamic CR somewhere around 8-8.25:1.

My question how high does the L2304F piston actually rise in the bore of the cylinder @ TDC? I am trying to figure out how high the piston actually rises in the cylinder so I can calculate the quench? The only specs they give for the piston are a compression height (Pin Height) of 1.56" and dome height of .100". If I add the rod length of 5.7" plus compression height of 1.56" I get 7.26". Is it correct to add 1/2 of the stroke to the 7.26"? That would put the top of the piston at 9.0" Is this the correct way to calculate this??

427Hotrod

Yes.

If you can spring for some aluminum heads (decent ones) go for it. That's where the power is.


JIM

kjr6306

Revi. Thanks for your input. I am going for the same look in my build. I want it to be close to stock looking as possible. Do you have any detonation with your set up? Are you using a .040 or .015 head gasket? With your cam specs it looks like your dynamic CR is at 8.78:1 which is a little on the high side for pump gas.

Can anyone else weigh in about the thought process for my build? Any suggestions for a cam. With a 4.11:1 rear end do I really need to be concerned with low end torque? Can I give up some low end for more top end in the 6-6500 rpm range? I also have a stock hood so I am limited on my intake options. I have the stock iron L-46 intake and an Edelbrock 2101 intake as my 2 options. Can I get any power out of the 2101 above 5500 RPM or is that the end of the line?

kjr6306

427... I know the power comes from the heads and cam but I cant even begin to think about that part of the build. The real point of this thread is to determine if the 11.0:1 pistons will be a good base to begin with??

LT-1 kid

I have had a few L46 engines rebuilt and always go with the stock 11:1 pistons
just use the best gas you can get in your area, I like high compresion sm chamber
head motors, and usung a 4-11 gear will give your very stout low end, but limit
the high end,

Revi

When you talk about 11:1 c/r, you do realize that a stock production L-46 coming down the assembly line at Flint didn't have an actual static 11:1 c/r. A typical undecked block will have the pistons sitting in the hole .025 or so. That's why most LT-1's/L-46's can run pump gas. (If you dynoed a typical Flint production L-46, it was probably in the 300hp-325hp range. The engines GM used for the dyno advertising numbers were "hand" built for the dyno, not your typical production engines/tolerances.)

To actually obtain a true static 11:1 c/r you will most likely need to "zero" the pistons with the deck, which will not run on pump gas.

My car is right on the edge for detonation. If I get a crappy load of 93oct I can/have gotten some detonation at 10/10ths throttle. I usually fill up at a Sunoco, but if I use an off brand station I have had some detonation issues. Once I accidentally filled up with 87oct, it detonated at partial throttle with that.

Solid LT1

Those TRW pistons are now made in India. I would look for a USA made Mahle, Weisco or CP piston with a far superior design to replace those TRW slugs. If you check Brezinski racing, they modify cast iron Qjet intakes to make more HP for circle track racing. David Vizard also had a book with details on modifying a Qjet intake to make decent power, with properly ported heads and intake your L-46 should run quite well.

bashcraft

Sure, if you drive the car like your Grandmother would.

You're disregarding one of the best pieces of advice given to you in this thread. Trying to run 11-1 compression with iron heads is stupid. With 93 octane it'll always be on the verge of detonation unless the timing is backed of to the point where performance is dismal. I've been there and almost destroyed the engine when I got some bad gas.

kjr6306

Revi - I realize that most of the LT-1/L-46 did not actually come from factory at 11:1. I plan on trying to measure and get an actual deck height to see where my block is. Can I not massage the CR with my head gasket thickness to get the desired .040 Quench? If the top of my pistons end up .025 in the hole, a .015 head gasket gets me where I need to be. What is the Dynamic CR of your engine with your cam?

Solid LT-1 - I plan on checking out the info David Vizard. Been reading good things about him...

Bashcraft - Of course I don't want to drive it like Grandma. I guess you missed the part of my post where I stated I may go with aluminum heads. The more I read about running 11:1, the more I am finding people that have no problems. Keeping Dynamic CR in the 8-8.25 range is the key. DO you understand this theory or are you just repeating info from someone on this forum that I dont believe is a reliable source.

Anyone else care to chime in on Static vs. Dynamic CR and its effect on detonation. Would like to hear some real world experiences....

bashcraft

I am giving you my experience with my '70 LT-1. The difference in power output when I went from 11-1 to 10-1 was insignificant. If anything, it ran a little better with 10-1 since I could advance the timing farther.

If for some reason you're in love with the idea of being able to claim you have 11-1 compression, go for it. Most people won't be impressed.

c3_dk

I've been fighting with my L46 for years now, I've had detonation a lot !
I tried a lot, cold sprak plugs, never used vacuum, 160F, ec ec

Now I mounted AFR 195 75cc heads, Fel-pro 0.015 => 10.04:1 and 8.13:1, right now have NO problems for the first time in years.

Before I used 99 octane EU Shell Classic gas (I think it is 94 or 95 US gas)
Now I can drive using 95 EU std. gas (91 US gas I think)

kjr6306

Bash - You really didn't answer my question....Do you understand the difference between Static and Dynamic CR? What are your cam specs and what is your Dynamic CR? I am trying to find the best bang for buck pistons. The Mahle, Weisco and Carillo brands are all $750 for a set. As mentioned, I am on a budget. The TRW pistons are forged dome and run $350. Compression ratio specs for a 64cc head is 10.5:1 or so depending on the actual block height. This seems like a pretty good compromise for the price. Anything less expensive is hypereutectic material....

kjr6306

C3 DK - Thats the kind of info I am looking for!! Your dynamic CR is right in the optimal range at 8.1. Thanks for the input!! Anyone else running 10.5 - 11.0:1 Static and around 8.0 Dynamic CR having any issues with detonation??

bashcraft

Yes, I do. Do you understand anything about matching engine components?

You are trying to build an engine cheap and purposely mismatching components to try make something sort of work.

Using cheap high compression pistons and a cam with more duration in order to lower the dynamic CR is just a Band-Aid.

Why do you feel you need forged instead of hypers?

c3_dk

I'm happy going from 11:1 to 10.04:1 / 8.13:1
With new AFR alu. heads, with bigger valves and MUCH flow, hydr roller cam with roller lifters, 1.6 Rocker Arms, then I've got a engine that can take some whipping, without detonation, and I have more power now, then before.

I think I could go to 10.5:1 or a bit more due to using alu heads without detonation, but I wanted to "play safe"
And I like to end at 0.040 quench witch I did with the 10.04:1 "setup"

c3_dk

No problem I'm glad to help.
BTW the cam I used was Comp Cams 12 466 8 (EFI cam)

kjr6306

Bash....you are exactly the type of person on here that I do not need any info from. You have nothing beneficial to add. Do me a favor.....don't respond to this thread anymore.

bashcraft

Truth hurts, huh?

BTW, you didn't answer my question. Why do you think you need forged over hypers? A set of flat top hypers would solve your problems.